The present invention relates to an electron-emitting source and, more particularly, to a field emission type electron-emitting source in which electron emission uniformity is improved, an electron-emitting module, and a method of manufacturing an electron-emitting source.
In recent years, a field emission type electron-emitting source using carbon nanotubes attracts attention as an electron-emitting source in a fluorescent display device such as an FED (Field Emission Display) or vacuum fluorescent display. In a carbon nanotube, a graphite single layer is cylindrically closed, and a 5-membered ring is formed at the distal end of the cylinder. Since the carbon nanotube has a typical diameter of as very small as 10 nm to 50 nm, upon application of an electric field of about 100 V, it can field-emit electrons from its distal end. Carbon nanotubes are classified into those with a single-layered structure described above and those with a coaxial multilayered structure in which a plurality of graphite layers stacked to form a telescopic structure are cylindrically closed. Either carbon nanotube can be used to form an electron-emitting source.
A field emission type electron-emitting source using conventional typical carbon nanotubes is formed of a flat substrate electrode in which many carbon nanotubes are arranged. When a high voltage is applied across this substrate electrode and a mesh-like electron extracting electrode opposing it, the electric field is concentrated to the distal ends of the carbon nanotubes to emit electrons from there. For this purpose, it is desirable that the carbon nanotubes on the substrate electrode have distal ends perpendicular to the substrate surface. If the electron emission uniformity is poor, luminance nonuniformity occurs. Therefore, it is desirable that the carbon nanotubes are uniformly arranged on the substrate electrode.
To form such an electron-emitting source, a method of forming carbon nanotubes directly on a flat substrate by using CVD (Chemical Vapor Deposition) is proposed. According to this method, an electron-emitting source made up of carbon nanotubes extending perpendicularly from the substrate surface and formed uniformly on the substrate can be manufactured.
In the conventional electron-emitting source obtained by directly forming carbon nanotubes on the substrate surface, however, a discontinuous portion such as a projection or recess sometimes exists. In this case, if a parallel electric field is applied to obtain field electron emission, the electric field is concentrated to the discontinuous portion to cause local electron emission, leading to a luminance nonuniformity on the fluorescent display device.
When the field strength is increased to improve the luminance, an electron-emitting density of a local portion exceeds the allowable limit to break this local portion, and a new field concentrated portion is formed around the broken portion. Consequently, breakdown occurs in a chain manner. This is the largest issue in actually applying field electron emission to a fluorescent display device.
It is an object of the present invention to provide an electron-emitting source which can obtain uniform field electron emission with a high current density, an electron-emitting module, and a method of manufacturing an electron-emitting source.
It is another object of the present invention to provide an electron-emitting source which does not cause a breakdown chain when the field strength is increased, an electron-emitting module, and a method of manufacturing an electron-emitting source.
In order to achieve the above objects, according to the present invention, there is provided an electron-emitting source comprising a substrate made of a material containing a metal serving as a growth nucleus for nanotube fibers as a main component and having a plurality of through holes, and a coating film constituted by nanotube fibers formed on a surface of the substrate and wall surfaces of the through holes.